BeidouMeo.java
/* Copyright 2002-2020 CS GROUP
* Licensed to CS GROUP (CS) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* CS licenses this file to You under the Apache License, Version 2.0
* (the "License"); you may not use this file except in compliance with
* the License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package org.orekit.gnss.attitude;
import org.hipparchus.RealFieldElement;
import org.hipparchus.util.FastMath;
import org.hipparchus.util.MathUtils;
import org.orekit.frames.Frame;
import org.orekit.time.AbsoluteDate;
import org.orekit.time.FieldAbsoluteDate;
import org.orekit.utils.ExtendedPVCoordinatesProvider;
import org.orekit.utils.TimeStampedAngularCoordinates;
import org.orekit.utils.TimeStampedFieldAngularCoordinates;
/**
* Attitude providers for Beidou Medium Earth Orbit navigation satellites.
* @author Luc Maisonobe Java translation
* @since 9.2
*/
public class BeidouMeo extends AbstractGNSSAttitudeProvider {
/** Limit for the Yaw Steering to Orbit Normal switch. */
private static final double BETA_YS_ON = FastMath.toRadians(4.1);
/** Limit for the Orbit Normal to Yaw Steering switch. */
private static final double BETA_ON_YS = FastMath.toRadians(3.9);
/** Simple constructor.
* @param validityStart start of validity for this provider
* @param validityEnd end of validity for this provider
* @param sun provider for Sun position
* @param inertialFrame inertial frame where velocity are computed
*/
public BeidouMeo(final AbsoluteDate validityStart, final AbsoluteDate validityEnd,
final ExtendedPVCoordinatesProvider sun, final Frame inertialFrame) {
super(validityStart, validityEnd, sun, inertialFrame);
}
/** {@inheritDoc} */
@Override
protected TimeStampedAngularCoordinates correctedYaw(final GNSSAttitudeContext context) {
// variation of the β angle over one orbital period (approximately)
final double beta = context.beta(context.getDate());
final double approxPeriod = 2 * FastMath.PI / context.getMuRate();
final double betaVariation = beta - context.beta(context.getDate().shiftedBy(-approxPeriod));
final double delta = context.getOrbitAngleSinceMidnight();
if (FastMath.abs(beta) <= BETA_YS_ON - FastMath.abs(betaVariation)) {
// the β angle is lower than threshold for a complete orbital period
// we are for sure in the Orbit Normal (ON) mode
return context.orbitNormalYaw();
} else if (FastMath.abs(beta) > BETA_ON_YS + FastMath.abs(betaVariation)) {
// the β angle is higher than threshold for a complete orbital period,
// we are for sure in the Yaw Steering mode
return context.nominalYaw(context.getDate());
} else {
// we are in the grey zone, somewhere near a mode switch
final boolean absBetaDecreasing = beta * betaVariation <= 0.0;
if (absBetaDecreasing) {
// we are going towards the β = 0 limit
if (FastMath.abs(beta) >= BETA_YS_ON) {
// we have not yet reached the far limit, we are still in Yaw Steering
return context.nominalYaw(context.getDate());
}
} else {
// we are going away from the β = 0 limit
if (FastMath.abs(beta) <= BETA_ON_YS) {
// we have not yet reached the close limit, we are still in Orbit Normal
return context.orbitNormalYaw();
}
}
// there is a mode switch near the current orbit, it occurs when orbit angle is 90°
// we check what was the β angle at the previous quadrature to see if the switch
// already occurred
final double angleSinceQuadrature =
MathUtils.normalizeAngle(delta - 0.5 * FastMath.PI, FastMath.PI);
final double timeSinceQuadrature = angleSinceQuadrature / context.getMuRate();
final AbsoluteDate quadratureDate = context.getDate().shiftedBy(-timeSinceQuadrature);
final double betaQuadrature = context.beta(quadratureDate);
if (absBetaDecreasing) {
// we are going towards the β = 0 limit
if (FastMath.abs(betaQuadrature) <= BETA_YS_ON) {
// we have switched to Orbit Normal mode since last quadrature
return context.orbitNormalYaw();
}
} else {
// we are going away from the β = 0 limit
if (FastMath.abs(betaQuadrature) <= BETA_ON_YS) {
// β was below switch at last quadrature, we are still in the Orbit Normal mode
return context.orbitNormalYaw();
}
}
return context.nominalYaw(context.getDate());
}
}
/** {@inheritDoc} */
@Override
protected <T extends RealFieldElement<T>> TimeStampedFieldAngularCoordinates<T> correctedYaw(final GNSSFieldAttitudeContext<T> context) {
// variation of the β angle over one orbital period (approximately)
final double beta = context.beta(context.getDate()).getReal();
final double approxPeriod = 2 * FastMath.PI / context.getMuRate().getReal();
final double betaVariation = beta - context.beta(context.getDate().shiftedBy(-approxPeriod)).getReal();
final double delta = context.getOrbitAngleSinceMidnight().getReal();
if (FastMath.abs(beta) <= BETA_YS_ON - FastMath.abs(betaVariation)) {
// the β angle is lower than threshold for a complete orbital period
// we are for sure in the Orbit Normal (ON) mode
return context.orbitNormalYaw();
} else if (FastMath.abs(beta) > BETA_ON_YS + FastMath.abs(betaVariation)) {
// the β angle is higher than threshold for a complete orbital period,
// we are for sure in the Yaw Steering mode
return context.nominalYaw(context.getDate());
} else {
// we are in the grey zone, somewhere near a mode switch
final boolean absBetaDecreasing = beta * betaVariation <= 0.0;
if (absBetaDecreasing) {
// we are going towards the β = 0 limit
if (FastMath.abs(beta) >= BETA_YS_ON) {
// we have not yet reached the far limit, we are still in Yaw Steering
return context.nominalYaw(context.getDate());
}
} else {
// we are going away from the β = 0 limit
if (FastMath.abs(beta) <= BETA_ON_YS) {
// we have not yet reached the close limit, we are still in Orbit Normal
return context.orbitNormalYaw();
}
}
// there is a mode switch near the current orbit, it occurs when orbit angle is 90°
// we check what was the β angle at the previous quadrature to see if the switch
// already occurred
final double angleSinceQuadrature =
MathUtils.normalizeAngle(delta - 0.5 * FastMath.PI, FastMath.PI);
final double timeSinceQuadrature = angleSinceQuadrature / context.getMuRate().getReal();
final FieldAbsoluteDate<T> quadratureDate = context.getDate().shiftedBy(-timeSinceQuadrature);
final double betaQuadrature = context.beta(quadratureDate).getReal();
if (absBetaDecreasing) {
// we are going towards the β = 0 limit
if (FastMath.abs(betaQuadrature) <= BETA_YS_ON) {
// we have switched to Orbit Normal mode since last quadrature
return context.orbitNormalYaw();
}
} else {
// we are going away from the β = 0 limit
if (FastMath.abs(betaQuadrature) <= BETA_ON_YS) {
// β was below switch at last quadrature, we are still in the Orbit Normal mode
return context.orbitNormalYaw();
}
}
return context.nominalYaw(context.getDate());
}
}
}